German astronomer and mathematician who was one of the first scholars to accept and teach Polish astronomer Copernicus's observation that the Earth orbits the Sun. One of Mästlin's pupils was German mathematician Johannes Kepler.
Mästlin was born in Göppingen, Baden-Württemberg, and studied at Tübingen. In 1580 he became professor of mathematics at Heidelberg and in 1584 at Tübingen, where he taught for 47 years.
In 1573, Mästlin published an essay concerning the nova that had appeared the previous year. Its location in relation to known stars convinced him that the nova was a new star - which implied, contrary to traditional belief, that things could come into being in the spheres beyond the Moon.
Observation of the comets of 1577 and 1580 convinced Mästlin that they also were located beyond the Moon. Together with other observations, this led him explicitly to argue against the traditional cosmology of Aristotle.
However, Mästlin's Epitome of Astronomy 1582, a popular introduction to the subject, propounded a traditional cosmology because this was easier to teach.